The groupings of electrical and fiber-optical connections within a single hybrid pair of connectors has not been accomplished until now without severe shortcomings, such as poor transmission of light, high resistance of the electrical contacts and excessive fragility. These shortcomings are particularly compounded when the hybrid connectors are used underwater or any other kind of severe environment.
The reasons for these defects can be found in fundamental and intrinsic difference between electrical and fiber-optical connections. In the case of electrical connectors, electrons must travel from one terminal to the next at select points and through layers of poorly conductive materials such as oxides. Good connections require contacts in which the mating parts slide against each other so as to remove by spalling part of the poorly conductive oxide material covering them. A reliable electrical contact must therefore exhibit what is known as a "wiping action". In most connectors where contact terminals are oriented axially, i.e. in the same direction as the direction of the electrical signals wiping action contacts are in a radial direction forcing the electrons to make two right-angle turns to go from one mating connector to the other.
On the other hand, to form a reliable optical signal connection, photons must travel in the same axial direction as the waveguide through lenses or fluids having the same index of refraction as the waveguide material. These requirements demand an exact control of the distance between the ends of the fiber's waveguides being coupled or their associated lenses. In an optical connector photons travel always in the same direction, while in an electrical connector electrons follow a multidirectional path. It is therefore quite apparent that the requirement of sliding electrical contacts and non-sliding, exactly positioned optical waveguides presents a unique problem in hybrid connectors which have not been adequately resolved.
Connectors designed for use underwater are often installed on the interfaces of structures which are subject to tremendous pressure differentials between the inside of the structure and the outside which is exposed to the water pressure. Connectors usually involve passing a conductor through the insulating body of a conductor from the back of the connector to the frontal interface where it forms a terminal designed to contact the terminal of the mating connector. If the pressure difference between the back of the connector and the mating interface exceeds the friction exerted by the body of the connector over the part of the conductor that passes through that body, the conductor or the terminal might be dislodged and fly out of the connector. This is a common occurrence when connectors are mounted on a bulkhead separating the inside of a deep sea probe from the surrounding waters and in other submarine structures. This requires that underwater connectors exhibit great mechanical simplicity and sturdiness. Furthermore, they should be extremely easy to use due to the fact that underwater manipulation is often impaired by the use of diving suits and that connections and disconnections are sometimes achieved by means of remote devices and robots. There is therefore an acute need for a type of underwater connector that could group both electrical and fiber-optical connections in a sturdy and easy-to-operate configuration.